{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE DeriveDataTypeable #-}
-- |
-- Module      : Data.Hourglass.Types
-- License     : BSD-style
-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
--
-- Basic times units and types.
--
-- While pratically some units could hold infinite values, for practical
-- and efficient purpose they are limited to int64 types for seconds
-- and int types for years.
--
-- Most units use the unix epoch referential, but by no means reduce portability.
-- the unix referential works under the Windows platform or any other platforms.
--
module Data.Hourglass.Types
    (
    -- * Time units
      NanoSeconds(..)
    , Seconds(..)
    , Minutes(..)
    , Hours(..)
    , TimeInterval(..)
    -- * Time enumeration
    , Month(..)
    , WeekDay(..)
    -- * Timezone
    , TimezoneOffset(..)
    , timezoneOffsetToSeconds
    , timezone_UTC
    -- * Computer friendly format
    -- ** Unix elapsed
    , Elapsed(..)
    , ElapsedP(..)
    -- * Human friendly format
    -- ** Calendar time
    , Date(..)
    , TimeOfDay(..)
    , DateTime(..)
    ) where

import Data.Int
import Data.Data
import Data.Ratio
import Control.DeepSeq
import Data.Hourglass.Utils (pad2)

-- | Represent any time interval that has an
-- equivalent value to a number of seconds.
class TimeInterval i where
    toSeconds   :: i -> Seconds
    fromSeconds :: Seconds -> (i, Seconds)

-- | Nanoseconds
newtype NanoSeconds = NanoSeconds Int64
    deriving (Read,Eq,Ord,Num,Data,Typeable,NFData)

instance Show NanoSeconds where
    show (NanoSeconds v) = shows v "ns"

instance TimeInterval NanoSeconds where
    toSeconds (NanoSeconds ns) = Seconds (ns `div` 1000000000)
    fromSeconds (Seconds s) = (NanoSeconds (s * 1000000000), 0)

-- | Number of seconds without a referential.
--
-- Can hold a number between [-2^63,2^63-1], which should
-- be good for some billions of years.
--
-- However, because of limitation in the calendar conversion
-- currently used, seconds should be in the range [-2^55,2^55-1],
-- which is good for only 1 billion of year.
newtype Seconds = Seconds Int64
    deriving (Read,Eq,Ord,Enum,Num,Real,Integral,Data,Typeable,NFData)

instance Show Seconds where
    show (Seconds s) = shows s "s"

instance TimeInterval Seconds where
    toSeconds   = id
    fromSeconds s = (s,0)

-- | Number of minutes without a referential.
newtype Minutes = Minutes Int64
    deriving (Read,Eq,Ord,Enum,Num,Real,Integral,Data,Typeable,NFData)

instance Show Minutes where
    show (Minutes s) = shows s "m"

instance TimeInterval Minutes where
    toSeconds (Minutes m)   = Seconds (m * 60)
    fromSeconds (Seconds s) = (Minutes m, Seconds s')
      where (m, s') = s `divMod` 60

-- | Number of hours without a referential.
newtype Hours = Hours Int64
    deriving (Read,Eq,Ord,Enum,Num,Real,Integral,Data,Typeable,NFData)

instance Show Hours where
    show (Hours s) = shows s "h"

instance TimeInterval Hours where
    toSeconds (Hours h)     = Seconds (h * 3600)
    fromSeconds (Seconds s) = (Hours h, Seconds s')
      where (h, s') = s `divMod` 3600

-- | A number of seconds elapsed since the unix epoch.
newtype Elapsed = Elapsed Seconds
    deriving (Read,Eq,Ord,Num,Data,Typeable,NFData)

instance Show Elapsed where
    show (Elapsed s) = show s

-- | A number of seconds and nanoseconds elapsed since the unix epoch.
data ElapsedP = ElapsedP {-# UNPACK #-} !Elapsed {-# UNPACK #-} !NanoSeconds
    deriving (Read,Eq,Ord,Data,Typeable)

instance Show ElapsedP where
    show (ElapsedP e ns) = shows e ('.' : show ns)

instance NFData ElapsedP where rnf e = e `seq` ()

instance Num ElapsedP where
    (+) = addElapsedP
    (-) = subElapsedP
    (ElapsedP e1 ns1) * (ElapsedP e2 ns2) = ElapsedP (e1*e2) (ns1*ns2)
    negate (ElapsedP e ns) = ElapsedP (negate e) ns
    abs (ElapsedP e ns)    = ElapsedP (abs e) ns
    signum (ElapsedP e ns) = ElapsedP (signum e) ns
    fromInteger i          = ElapsedP (Elapsed (fromIntegral i)) 0

addElapsedP :: ElapsedP -> ElapsedP -> ElapsedP
addElapsedP (ElapsedP e1 (NanoSeconds ns1)) (ElapsedP e2 (NanoSeconds ns2)) =
    let notNormalizedNS = ns1 + ns2
        (retainedNS, ns) = notNormalizedNS `divMod` 1000000000
    in  ElapsedP (e1 + e2 + (Elapsed $ Seconds retainedNS)) (NanoSeconds ns)

subElapsedP :: ElapsedP -> ElapsedP -> ElapsedP
subElapsedP (ElapsedP e1 (NanoSeconds ns1)) (ElapsedP e2 (NanoSeconds ns2)) =
    let notNormalizedNS = ns1 - ns2
        notNormalizedS  = e1 - e2
    in  if notNormalizedNS < 0
            then ElapsedP (notNormalizedS - oneSecond) (NanoSeconds (1000000000 + notNormalizedNS))
            else ElapsedP notNormalizedS (NanoSeconds notNormalizedNS)
  where
    oneSecond :: Elapsed
    oneSecond = Elapsed $ Seconds 1

instance Real ElapsedP where
    -- FIXME
    toRational (ElapsedP (Elapsed (Seconds s)) (NanoSeconds ns)) =
        fromIntegral s + (1000000000 % fromIntegral ns)

-- | Month of the year
data Month =
      January
    | February
    | March
    | April
    | May
    | June
    | July
    | August
    | September
    | October
    | November
    | December
    deriving (Show,Eq,Ord,Enum,Data,Typeable)

-- | Day of the week
--
-- the enumeration starts on Sunday.
data WeekDay =
      Sunday
    | Monday
    | Tuesday
    | Wednesday
    | Thursday
    | Friday
    | Saturday
    deriving (Show,Read,Eq,Ord,Enum,Data,Typeable)

-- | Offset against UTC in minutes
--
-- * a positive number represent a location East of UTC.
--
-- * a negative number represent a location West of UTC.
--
-- LocalTime t (-300) = t represent a time at UTC-5
-- LocalTime t (+480) = t represent a time at UTC+8
--
-- should be between -11H and +14H
newtype TimezoneOffset = TimezoneOffset
    { timezoneOffsetToMinutes :: Int -- ^ return the number of minutes
    } deriving (Eq,Ord,Data,Typeable,NFData)

-- | Return the number of seconds associated with a timezone
timezoneOffsetToSeconds :: TimezoneOffset -> Seconds
timezoneOffsetToSeconds (TimezoneOffset ofs) = Seconds (fromIntegral ofs * 60)

instance Show TimezoneOffset where
    show (TimezoneOffset tz) =
        concat [(if tz < 0 then "-" else "+"), pad2 tzH, pad2 tzM]
      where (tzH, tzM) = abs tz `divMod` 60

-- | The UTC timezone. offset of 0
timezone_UTC :: TimezoneOffset
timezone_UTC = TimezoneOffset 0

-- | human date representation using common calendar
data Date = Date
    { dateYear  :: {-# UNPACK #-} !Int   -- ^ year (Common Era)
    , dateMonth :: !Month                -- ^ month of the year
    , dateDay   :: {-# UNPACK #-} !Int   -- ^ day of the month, between 1 to 31
    } deriving (Show,Eq,Ord,Data,Typeable)

instance NFData Date where
    rnf (Date y m d) = y `seq` m `seq` d `seq` ()

-- | human time representation of hour, minutes, seconds in a day.
data TimeOfDay = TimeOfDay
    { todHour :: {-# UNPACK #-} !Hours   -- ^ hours, between 0 and 23
    , todMin  :: {-# UNPACK #-} !Minutes -- ^ minutes, between 0 and 59
    , todSec  :: {-# UNPACK #-} !Seconds -- ^ seconds, between 0 and 59. 60 when having leap second */
    , todNSec :: {-# UNPACK #-} !NanoSeconds -- ^ nanoseconds, between 0 and 999999999 */
    } deriving (Show,Eq,Ord,Data,Typeable)

instance NFData TimeOfDay where
    rnf (TimeOfDay h m s ns) = h `seq` m `seq` s `seq` ns `seq` ()

-- | Date and Time
data DateTime = DateTime
    { dtDate :: Date
    , dtTime :: TimeOfDay
    } deriving (Show,Eq,Ord,Data,Typeable)

instance NFData DateTime where
    rnf (DateTime d t) = rnf d `seq` rnf t `seq` ()